Abstract The hydrogen bonding structure of water and its dynamics in aqueous ammonia solution is investigated by using classical molecular dynamics simulations. We have considered eight different mole-fraction of ammonia, ranging from x N H 3 = 0.02 to 0.30, and the pressure variation is carried out on the concentrated ammonia solution ( x N H 3 =0.30), ranging from P = 0.1 MPa to 800 MPa, at 293K. The radial distribution function indicates that the addition of ammonia facilitates the structural organization of water, which is further supported by increasing values of asphericity parameter. But, the tetrahedral order parameter values suggest an angularly disordered arrangement of water molecules. The self-diffusion coefficient values of water pass through shallow minima, whereas it increases for ammonia with ammonia concentration in the solution. The application of pressure causes a sharp decline in translation mobility of ammonia compared to water, but at very high pressure (above 600 MPa), both the species diffuse at the same rate. The rotational relaxation of ammonia is approximately three times faster than water in the solution, which further increases along with concentration as well as pressure. A similar trend is also observed in the case of structural reorganization of water-water and water-ammonia hydrogen bonds. The water-water and water-ammonia hydrogen-bond lifetimes are increasing with ammonia concentration, whereas it passes through shallow maxima with the application of pressure. In this study, we have compared two different Lennard-Jones (LJ) combination rule, which causes negligible differences in the calculated properties. The solvation scenario of different ionic (Na+, Cl−) and neutral (Cl0) solutes are also analyzed along with the coordination number. It is observed that the hydration shell of ion is mainly dominated by water molecules in the solution.

中文翻译：

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浓度和压力对氨水溶剂化结构和水-氨混合物中依赖于组成的离子溶剂化场景的影响

摘要 利用经典分子动力学模拟研究了水的氢键结构及其在氨水溶液中的动力学。我们考虑了八种不同摩尔分数的氨，范围从 x NH 3 = 0.02 到 0.30，压力变化是在浓氨溶液 (x NH 3 =0.30) 上进行的，范围从 P = 0.1 MPa 到 800 MPa ，在 293K。径向分布函数表明氨的加入促进了水的结构组织，这进一步得到了非球面参数值的增加的支持。但是，四面体顺序参数值表明水分子的角度无序排列。水的自扩散系数值通过浅层最小值，而随着溶液中氨浓度的增加，它会增加。与水相比，施加压力会导致氨的平移迁移率急剧下降，但在非常高的压力下（600 兆帕以上），两种物质以相同的速率扩散。氨的旋转弛豫速度大约是溶液中水的三倍，并且随着浓度和压力的增加而进一步增加。在水-水和水-氨氢键的结构重组的情况下也观察到类似的趋势。水-水和水-氨氢键寿命随着氨浓度而增加，而随着压力的施加，它会通过浅层最大值。在这项研究中，我们比较了两种不同的 Lennard-Jones (LJ) 组合规则，这导致计算属性的差异可以忽略不计。不同离子（Na+、Cl−) 和中性 (Cl0) 溶质也与配位数一起分析。观察到离子的水合壳层主要由溶液中的水分子控制。